Alzheimer's disease is a neurodegenerative disease caused by accumulation of a causative substance such as β-amyloid in brain, causing damage to nerve cells. Although the number of patients suffering from Alzheimer's disease is expected to increase upon the advent of an aging society, prophylactic agents and therapeutic agents for the disease are hardly available, and development of new prophylactic agents, therapeutic agents, vaccines and the like has been demanded. Vaccines against Alzheimer's disease have been developed using β-amyloid, which is a causative substance of the disease, as an antigen, but development of the vaccines was difficult because of problems such as side effects. Therefore, development of a vaccine using a β-amyloid antigenic determinant (epitope) which does not cause side effects, and establishment of mass production techniques for the vaccine are required.
Soybean is an exalbuminous seed, which does not have albumen and accumulates its nutrition in the germ corresponding to the cotyledon. About 40% of the whole volume of a seed, which corresponds to the germ, is occupied by storage proteins. Therefore, soybean has characteristics as a storage tissue different from those of other crops such as rice and maize that accumulate starch in albumen as a major reserve substance, so that it is a crop suitable for being made to produce and accumulate an exogenous protein. The major seed storage proteins in soybean are 11S globulin (glycinin) and 7S globulin (β-conglycinin). The spatial structures of these seed storage proteins and the mechanisms of their accumulation in the cell have been elucidated, and it is known that the genes encoding them have portions called variable regions. It is thought that the spatial structures of the proteins can be maintained even after insertion of an exogenous gene into the variable regions and that the properties of the storage proteins are not affected by such insertion.
In general, a β-amyloid antigenic determinant is a protein (peptide) having a relatively low molecular weight composed of several amino acids, and it has been difficult to make the peptide highly accumulated in seeds of a transformed soybean for the purpose of mass production of the peptide by introducing a gene encoding the peptide to the soybean, since the peptide was degraded by enzymes such as proteases in the cells.
On the other hand, as transformed crops that accumulate biologically active peptides and vaccines in their seeds, a transformed soybean that accumulates a hypotensive peptide (Patent Document 1), a transformed rice that accumulates a vaccine against allergy to cedar pollen (Patent Document 2), a potato that produces β-amyloid (Non-patent Document 1) and a tomato that produces β-amyloid (Non-patent Document 2) are known.
However, a transformed soybean that highly accumulates an Alzheimer's disease vaccine composed of a β-amyloid antigenic determinant (epitope), and mass production techniques for the vaccine using the soybean have not been known so far.
Common bean is a plant belonging to Leguminosae, to which soybean also belongs, and the content of protein in a seed of common bean is 20%. It is known that arcelin, which is one of the major seed storage proteins in common bean, can be divided into plural types, that is, arcelin 1 to 7, and that the homologies among the nucleotide sequences of the part encoding their structural proteins are high. The structures of the arcelin proteins in common bean have been less analyzed compared to those in soybean, and only the spatial structures of arcelin 1 and 5 have been revealed.
Further, it is known that prolamin, which is one of the major seed storage proteins in rice, is an indigestible protein which can be divided into several types (e.g., 10K, 13K and 16K) having different molecular weights. The spatial structure of prolamin has not been revealed.